This invention relates to an electro-thermal fluid displacement actuator in general and to a ported insert partition for such an actuator having a positive temperature coefficient heater in particular.
In copending, co-assigned Huebscher application Ser. No. 623,669, filed Oct. 20, 1975, an electro-thermal linear actuator is disclosed and claimed in which a resistance type heating element is positioned in a variable volume chamber containing a fluid which undergoes a liquid to gas phase change upon being heated. Such phase change is used to increase the pressure in the variable volume chamber formed in part by an elastomeric diaphragm, with such increased pressure driving the diaphragm and piston assembly connected thereto through an expansion stroke. Upon the de-energization of such resistance heater, the fluid cools down to decrease the pressure in the variable volume chamber permitting a spring to return the piston assembly and diaphragm to the unexpanded inboard condition. The operational performance of the above-described electro-thermal linear actuator has been operationally quite satisfactory. However, over extended periods of use, the elastomeric diaphragm may age and undergo property changes caused by exposure to the high fluid temperatures involved, with such high temperatures causing permeation of the fluid through the elastomer. Moreover, the submerged resistance type heating element, if continuously energized during an actuator cycle, continues to increase in temperature resulting in damage either to the element itself or to the actuator assembly.
Reference may also be made to Schweitzer U.S. Pat. No. 3,132,472 wherein a thermal actuator for valves or the like is disclosed. Such actuator includes a substantially completely filled pressure vessel in which an open bottom, bell shaped member is positioned to define the boiler chamber therewithin, such boiler chamber directly communicating with the vessel through its open bottom.